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Tooth movement by almuzian ok ok
Tooth movement by almuzian ok ok
Tooth movement by almuzian ok ok
Tooth movement by almuzian ok ok
Tooth movement by almuzian ok ok
Tooth movement by almuzian ok ok
Tooth movement by almuzian ok ok
Tooth movement by almuzian ok ok
Tooth movement by almuzian ok ok
Tooth movement by almuzian ok ok
Tooth movement by almuzian ok ok
Tooth movement by almuzian ok ok
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Tooth movement by almuzian ok ok

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  • 1. Tooth movement Tooth Exfoliation The resorption process involved in exfoliation is not constant; there are episodes of resorption alternating with periods of repair. There are four causes of exfoliation of the primary dentition: 1. Cementoclastic activity of permanent teeth: The erupting permanent teeth exert pressure on the surrounding bone, causing the differentiation of osteoclasts. These in turn resorb the roots of the primary teeth; this shortens the roots and causes loss of attachment of the periodontal ligament. 2. Follicular effect of permanent teeth: Where teeth have been experimentally wired to prevent eruption, bone resorption has continued leading to cystic cavities. It appears therefore that resorption is the rate-limiting step and is signalled for by the follicle of the erupting tooth. 3. Alveolar bone growth: continued growth of the alveolar bone results in loss of structural support of the deciduous teeth. 4. Increased force of mastication: increased masticatory forces on the weakened teeth, causes increased compression of the periodontal ligament and encourages resorption of primary teeth and alveolar bone. Eruption Phases of eruption 1. Pre-eruptive - movements made by tooth germs prior to eruption 2. Eruptive - tooth movement into functional occlusion (rate of eruption is about 0.3mm - 1mm a month initially) it starts when the root start to develop, and at the
  • 2. same time the primary tooth successor and bone resorbed allowing eruption of the tooth. There are many theories on how the eruptive mechanism is generated: A. Genetic component – e.g. disturbed eruption in disorders of enamel formation and gingival overgrowth, and syndromes with growth retardation i.e. cleidocranial dysplasia B. Follicular theory- force comes from the follicle, which probably has many cytokines and growth factors. Removal of the dental follicle results in complete cessation of eruption. Furthermore if a silicone replica of a tooth is used to replace a normal tooth during its development, eruption still occurs as long as the follicle remains intact. C. Root growth - the crown moves occlusally because of root growth, but rootless teeth still erupt. D. Alveolar bone growth - excessive bone is formed beneath crypts of erupting teeth. E. Periodontal ligament -good evidence suggests that periodontal ligament fibroblasts are capable of generating contractile forces, pulling the tooth in an occlusal direction. But, teeth still erupt when the periodontal ligament is disrupted. F. Hydrostatic forces - these are generated either within the pulp or by the apical vasculature. This localized force is responsible for pushing the tooth in an occlusal direction. However, teeth still erupt when their pulp is removed, and hypertensive drugs seem to have no effect on eruption. 3. Posteruptive movement - (approximately 0.4mm per annum). There is many reasons for posteruptive movement including:
  • 3. A. Accommodation for growth - these movements occur to accommodate the final growth of the jaws. This is usually complete by the late teens. The amount of growth required is best seen by observing the effects of an ankylosed tooth. B. Compensation for occlusal wear C. Accommodation for proximal wear. Theories of orthodontic movements 1. Bone bending. (Piezo-electric forces) Bone remodeling occurs when the bone matrix distorted by applied force, (In fact the crown moves 10x more than the periodontal width due to bone bending) so the osteocyte send a signal to the superficial osteoblast that will recruit osteoclast by OPG-RANKL-RANK mechanism to start bone remodeling. Bending bone can cause two classes of stress-generated electrical effects according to Wolff's Law. 2. Pressure-tension hypothesis • Areas of compression where capillary blood pressure is not exceeded i. Capillaries remain patent. ii. Cells of the periodontal ligament proliferate. iii. On the pressure side osteoclasts are recruited and cause bone resorption. • Areas of compression where capillary blood pressure is exceeded locally i. Capillaries are completely occluded. ii. Cells of the periodontal ligament die, and the area becomes structureless or "hyalinised" assuming a ground glass appearance.
  • 4. iii. In this situation a different type of resorption is seen whereby osteoclasts appear to 'undermine' bone rather than resorbing at the 'frontal edge' • Areas of tension i. Periodontal ligament width is increased, ii. Fibres are lengthened and periodontal ligament fibroblasts proliferate. iii. Osteoprogenitor cells also proliferate and differentiate into osteoblasts laying down osteoid, which calcifies to form bone. • Areas of excessive tension i. Periodontal fibres are torn and capillaries rupture, causing hemorrhage into the periodontal ligament. ii. The principle fibres of the periodontal ligament rapidly adapt to the new tooth position, but trans-septal and free gingival fibres do not. iii. Residual tension in these fibres may contribute to relapse following rotation. iv. In order to counteract this, pericision may be undertaken to reduce rotational relapse. 3. Hydrodynamic theory  It is the weakest theory  It claims that the force is transferred to the bone via pd fibers, cell and fluid.  The weakness is that the pd space is closed box. 4. Biomechanical/cellular response theory,
  • 5. • The application of a force to a cell membrane triggers off a number of responses including subsequent metabolism of arachidonic acid. • These stimulate second messengers and elicit a cell response. (Cells have internal signaling systems, which convert external stimuli, such as hormones or mechanical forces (first messengers) into internal signals, the so called second messengers) • These transduce signals from the cell membrane to the inside of the cell and ultimately to the nucleus. There are three main second messenger systems. These are elevated by mechanical forces and have been implicated during orthodontic tooth movement: • cAMP (cyclic adenosine 3',5' - monophosphate) • inositol phosphates • tyrosine kinases During tooth movement, the second messengers evoke a nuclear response, which will either result in production of factors responsible for osteoclast recruitment and activation, or bone forming growth factors. Optimal force level in orthodontics Optimal force level in orthodontics defined as a mechanical input that leads to maximum rate of tooth movement with minimal irreversible damage to the root, periodontal ligament and alveolar bone. The theory of optimum forces was proposed by Storcy and Smith in 1952.
  • 6. Force threshold is defined as the minimum force to produce movements. Classically, ideal forces in orthodontic tooth movement are those that just overcome capillary blood pressure 20-25gm/cm3 as per Schwartz (1932). • Quinn & Yoshikawa, 1985 mentioned four theories regarding force magnitude 1. Hypothesis 1 shows a constant relationship between rate of movement and stress. The rate of movement does not increase as the stress level is increased. However no studies support this theory. 1. Hypothesis 2 is more complex. The relationship here calls for a linear increase in the rate of tooth movement as the stress increases. Hypothesis 2 is difficult to disprove because most studies used only two force magnitudes and were unable to describe the behaviour of the curve as the stress reached higher levels (Johnston 1967). 2. Hypothesis 3 depicts a relationship in which increasing stress causes the rate of movement to increase to a maximum. Once this optimal level is reached, additional stress causes the rate of movement to decline. This hypothesis was originally proposed by Smith and Storey 1952. The available literature suggests that hypothesis 3 may not be an accurate representation of the data. This had been supported later by Lee 1995
  • 7. 3. Hypothesis 4 is a composite of some of the foregoing concepts. Here the relationship of rate of movement and stress magnitude is linear up to a point; after this point an increase in stress causes no appreciable increase in tooth movement. This had been supported later by Owman-Moll 1996 and King 1991. From the study of Samuel 1998 who compared in his RCT between 100gm and 200gm NiTi sprin and also used the historical data from his previous study in 1993. Samuel in 1998 found that there is no difference between 150gm and 200gm but a significant difference between the last two forces and 100gm. The existing clinical data may best support the interpretation provided in hypothesis 4. However, • Pilon (1996), working on Beagle dogs, showed that the rate of tooth movement and amount of OA loss were not significantly different for forces from 50g to 200g. In some dogs, teeth moved quickly while in others, teeth moved slowly, regardless of the forces used. The rate of movement was highly correlated between right and left sides in each dog, suggesting that inherent metabolic factors may be much more important than force level in determining the rate of movement of the teeth (including those in the OA unit). However, Pilon (1996) found that rate of tooth movement was still related to root surface area, as the OA units moved less than the teeth being moved. Therefore, there is some scientific support for the differential force theory, but the exact extent of its influence is unknown. • Other studies have shown that similar individual variation in orthodontic response to applied force also appears to occur in humans (Hixon 1969, Hixon 1970). This variation is due to variable cellular activity and density of the bone. This is why
  • 8. the movement through the cortical bone or in adults is slow due to reduced cellular activity and dense bone. • Ren et al. 2004 systematic review showed insufficient data to determine whether there is a threshold of force below which tooth movement does not occur. They also identified a wide range of forces (104–454 gm) over which the maximum rate of movement could be achieved. Mechanical factors in tooth movement A. Magnitude Type of tooth movement Force for single rooted teeth in gm Force for multirooted teeth in gm Tipping 35 60 Bodily movement 70 120 Root uprighting 50 100 rotation 35 60 Extrusion 35 60 intrustion 10 20
  • 9. B. Force distribution and type of movement C. Root surface area D. Duration Drug effect on response to orthodontic force It has been proved that pharmacological agents manipulate tooth movement. Drugs that stimulate the orthodontic tooth movement are: 1. Vitamin D administration can enhance the response to orthodontic force. 2. Direct injection of PG into the PDL has been shown to increase the rate of tooth movement, but this quite painful. Drugs that are known to inhibit tooth movement 1. Bisphosphonates Bisphosphonates are used to treat bone metabolism disorders such as osteoporosis, Paget’s disease, and bone metastasis. Bisphosphonates bind strongly to the bone mineral hydroxyapatite (Jung et al., 1973) and inhibit bone and root resorption.
  • 10. 2. PG inhibitors. These can be divided into two categories: A. Corticosteroids reduce PG synthesis by inhibiting the formation of arachidonic acid; B. NSAIDs inhibits the conversion of arachidonic acid to PGs. C. Several other classes can affect PG levels and therefore could affect the response to orthodontic force. • Tricyclic antidepressants, An anticonvulsant drug (phenytoin) has been reported to decrease tooth movement in rats. • Anti-arrhythmic agents, • Anti-malarial drugs, • Methyl xanthines fall into this category. • Tetracycline. D. Recently there is an interest in the use of micro-osteoperforations to speed tooth movement. Alikhani et al 2013 Reason why roots do not normally resorb A. Cementum has anti-angiogenic properties (avascular). This means blood vessels are not formed adjacent to cementum and less osteoclasts will be present there. B. Periodontal ligament fibres are inserted more densely in cementum than alveolar bone and thus osteoclasts have less access to the cemental layer. C. Cementum is harder than bone and more densely mineralized.
  • 11. D. Cemental responsive to systemic factors such as parathyroid hormone rather than local factors. Mechanical basis of tooth movement The following are important concepts and definitions pertaining to orthodontic tooth movement and are relevant to its understanding: • Force—a load applied to an object that has both magnitude and direction. Forces can be represented visually by vectors. • Centre of resistance—the point at which bodily movement or translation of an object will result when a force is applied. In a free-floating body, the center of resistance coincides with the center of mass; however, teeth are fixed in bone and therefore, the centre of resistance is difficult to determine accurately. It is generally presumed to be located around one-third to halfway down the root of a healthy single-rooted tooth. The centre of resistance will move apically if bone support is lost due to periodontal disease .For a multirooted tooth, the centre of resistance is between the roots, 1 to 2-mm apical to the furcation • Moment—when a force is applied to a body at a distance from the centre of resistance a rotational effect or moment is created . It is the product of the force and the distance from the centre of resistance, so the greater the distance the greater the rotation. • Couple—this represents two equal and opposite forces. A couple exerts no net force to bodily move a tooth, as the forces are opposite in direction and cancel each other out. A couple acting alone on a tooth will produce a purely rotational
  • 12. movement , whilst a couple combined with an additional force can produce bodily movement • Friction: In clinical practice with fixed appliances, friction is affected by a number of factors: 1. The chemical and physical interaction of the archwire 2. The composition of the bracket itself 3. The angle of contact between archwire and bracket slot—teeth do not slide along brackets, but tip and then upright as the crowns are displaced initially a greater amount than the roots. This results in an increase in the angle of contact between archwire and slot, which increases friction and binding between archwire and bracket. This is affected by the width of the bracket, with narrower brackets having been reported to result in greater friction—presumably as they allow greater tipping & binding. 4. Type of ligation—elastomeric ligation and tightly secured steel ligatures will increase friction. Self-ligating brackets, which secure the wire via a clip or gate, have been shown to reduce friction in laboratory studies.

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